Porous abrasive article



Mays, 1944;

l H. R. l-loucl-uNsA 2,348,474

POROUS ABRASIVE ARTICLE 2 'sheets-sheet 2 Filed Feb. '2, 1942 bly( iorn y Patented A9, 19,44

, l l 2,348,474 Y PoRoUs anaslvn aa'rlcmA j l'Henry R. Houchins, Niagara Falls, N. Y., asslgnor to The CarborundumCompany, Niagara Falls,

' N. Y., a `corpo raticm of Delaware 'Applicautarebrum 2, 1942, serial No. 429,288

14 claims.

The invention of this application relates to theformation of abrasive wheels and particularly to abrasive wheelsof the type known as" snag faces as ings.

`f tliejobjects offthe present inven lfnpatible Lwith. fastfgrinding action, but withbut'the' use of fine abrasive particles to fill ing inthe removalof 'irregularitiesjfrorn` the surduce a wheel 'with vthe maximum denor vat in which is contained a slip or slurry II` of a ceramic bonding material.L A ring or tube I2, of metal orother suitable material, is provided with lugsV I3 near the-bottom thereof and extending inwardly. Resting upon lugs I3 is a perforated plate or disc I4 on which rests a ne a screenfl, adapted to support a body or mass of abrasive I6. Resting upon Vabrasive grain I6 is 1 another screen l1 anda vperforated plate or disc thefspacesbetween theA `larger abrasive grains. l Qtheiobiects of the invention are'to `obtain com@ j paratively high porosity fi'n an abrasive wheel while maintaining high' density and high strength,`

tofproduce an abrasive wheelyc'ontaining 'the maximum possible number of active abrasive grains per'unii;v of grinding area, andY to avoid breakingthelarge grains of abrasive. l

It is at present customary` to `manufacture '1 snagging wheels by pressing a 'damp mixture o! abrasive 'and bond. The mixture contains a ratherihigh proportion'of` bond and a long range of sizes of abrasive particles in order to obtainrsufcient density' to cause` resistance to Wear inl thehard service ,to 'which such wheels are subjected. The cutting 1rate of snagging Awheels made according to this procedure is adverselyl affected, however, sincefthe long range of grit sizes and the comparativelydarge quantity of nner grains reduceslthe number of active abra- I8. Tube or ring I2 may conveniently be and is preferably split, as at I9,to` facilitate -the'remo'val of the abrasive Wheel aftervit, is Aformed. In carrying out the present invention with the `apparatus shown in `Figure I1, a suitable ceramic bond 'is chosen and the ingredients thereof are formed into a slip orslurry with water. This slip is placed in vat I0. Abrasive grain of the desired character and size-is placed in` tube I2 between plates I4 and I8 and screenslS and I'I. The grain after being put in tube I2 is in what may be called a vertically self-supporting condition. Each grain must necessarily contact at least one other grain thus to be heldin position. After the top screen` I 1 and top plate I8are placed on top of the abrasive grain, the abrasive grain is compacted by any suitable means. A convenlent and satisfactory method of compacting the abrasive grain is by subjecting the tube I2 con f sive grains available inthe surface of the abra-f sive wheel.` In addition, .the high percentage of bond necessarily produces a separation of the:

abrasive grains'ard lls up1a 4considerable part of the space between the grains.v rSnag'ging wheels madeby the method ldescribed above thus have a tendency to lillV rapidly and become glazed when-muse.l '1; c

fuBy'the method of the present invention-fthe de cts of snagging'wheelsproduced'by the practic described above are corrected and'wheels hav- 'ghercutting rates and little.;tendency to m becomeglazed maybe easily produced. @In the accompanying drawingsrFlgurel isa some maine which f may be used in carrying fout,` the O'f w mibiffograph'of the structure of an. abrasive; el xii-'ade laccording to the methbdof theprese -f eitfi'n'vntin. f" vFutures 3 and 4-are photomicrof.:

hatv diagrammatic view of one form of 'ap-..

Whena mix of abrasive grain andbond is pressed in the normal manner of the prior art many of the larger grains are crushed and thus rendered less effective. By the present method of initially compacting the grain to maximum density all danger of crushing-or breaking the grain is avoided and the grai-nfis, toaconsiderable extent,formed into: an inter-lockingstruc ture.- Greater abrasive densityncanthusbemb-v,

tained than by the old methods of 'pressingvorf e' present invention; -:Figure l2 is ,a L

graphs of the structure `oi' abrasive wheels-prof"l duced'by the pressing method previously in use.

TA description lofthfe method or this inven-,z

,Y tion will be made with' lreferencetoFiure 1V off' puddling Vwhere l bond. keepsr the abrasive. grains apart. `Vibration .may'also ,have somefendency; to orient the grainitowardthe periphery of tube, M v 1- 5 f, ,1; wf.

Ringk ontube' I2 containing thecompactel grain is `then-"slowly` lowered into v 7tank or vvai-.flQSFQIJf-, taining theslipi I' *ofi ceramic bondfandfthe, slip L is vallowed totY ypenetrate upwardly` `through :the-

compacted l voi grainfffth'ef. .tube b elngtpree vented from resting directly on the bottomff` vat I 0i by l'feet" T2 Il, kconve'nientlyf fformed integrally withlthefsidesithereof,amhefhydrostaticpres,

any sumcient fte lrcase'fsthefslipvr slurry,

the drawings. In Figure' 1. 10 represents a tank 55 `pacted grain. If necessary to prevent displacebond with 66.5 parts by weight of water.

ment thereof the covering screen Il and plate I8 may be clamped in place or held down by a weight (not shown.

` sure of the slurry in vat III surrounding tube I2 is usually sufcient to cause the slurry to permeate the compacted mass of grain. In'cases where, because of the use of finer abrasive particles, a slip of high viscosity, or for other reasons, penetration of the grain bythe slurry is difficult or imperfect it has been found possible to'increase the speed and completeness of penetration in several ways. A preliminary treatment of the abrasive grain with a wetting agent .has been found very advantageous. subjecting tube I2 to vibration while it is immersed in vat I also hastens saturation of the granular mass with the slurry. If necessary, a bonnet or hood (not shown) can'be attached to the top of tube I2 and a slight reduction of pressure therein be employed to aid in penetration of the granular mass by the slurry.

The amount of bond in a wheel made by the method of the present invention, other variable factors being constant. is a function of the speeic gravity of the bonding slip or slurry. Since this specific gravity may be easily adjusted by varying the proportions of bond and water, the amount of bond in the wheel, and hence the hardness of the wheel, may be readily varied.

The following are typical examples of abrasive` wheels made by this process.

Example I Grain size distribution Parts by weight 16 grit silicon carbide 15 20 grit silicon carbide 55 y 24 grit silicon carbide 20 36 grit silicon carbide 10 Bond composition: Parts by weight Feldspar' n 60 Kaoline Ball clay 15 Flint 9 Talc l The abrasive grain` mixed thoroughly and placed in a tube or ring, such as that shown at I2 in Figure 1, of the proper diameter and is vibrated until it reaches its highest density, which is usually obtained after V2 to i minute of vibration. Y

The bond ingredients are mixed and formed into a slip by mixing 100 parts' by weight of The slip is thendeocculated to thegreatest possible degree with the necessary amount of a 50% sodium silicate solution. The amount of silicate necessary is. in general, of the order of .25 percent of the amount of dry bond. The resulting slip should have a specific gravity of The tube or grain is then lowered into the slip and allowed to sit therein until the slip covers the surface of upper plate I8. Obviously. the level of the slip II in vat I0 must be'highcr than plate Il yring* containing the compacted with tubo l2 in position in vot In. "rho tube or ring containing the abrasive grain saturated with slip v`is then withdrawn'from the vat containing the sup or slurry of bond, driedat 325 F., shaved to size and shape, and burned or red in a kiln at cone I2. Following the burning, the.

wheel is finished in the usual way. A wheel made in accordance with this example contains about 17% bond by weight. By increasing the specific gravity of the slip, wheels having as muchas 22% bond have been produced.

The following example exemplifies the formation of a snaggin'g wheel using fused alumina abrasive.

i Example II Grain size distribution: Parts by weight 14 grit fused alumina 50 16 grit fused a1umina 25 20 grit fused alumina. 25

Bond composition:

Albany slip clay.

The granular abrasive after being thoroughly mixed together is placed in a ring or tube of the proper diameter and, if desired, is compacted as above described in Example I by the use of vibration. The tubev containing the mass of grain is then lowered into a vat in which there vis a slurry or suspension ofthe Albany slip clay which has been made up with water to a specic gravity of 1.42. Suspension of the clay is maintained-by the use of a small amount of suitable deocculating agent such as, for example, a solution of sodium silicate. After the clay slurry has saturated the mass of grain, the tube containing the grain is withdrawn from the vat, dried at a moderate temperature, yfor example 300 F., and then, after being shaved to size and shape, burned or :Bred at approximately 1200 C.

The wheel produced by Example II is, as is customary with alumina snagging wheels, some.- what less hard and dense 'than the silicon carbide wheel produced by Example I. Of course the densityand hardness of the wheel could be increased by suitably varying the grit size of the abrasive, its degree of compactness or the specic gravity of the clay slurry and hence the amount of bond in the wheel.

As. win be evident. the invention or the l ing ingredients are adapted for use as a slurry or dispersion.

It has been found through tests that abrasive articles made by the method ofthe present invention have very much greater transverse strength and resistanceto impact than abrasive articles of the same composition, pressed in they manner of the prior art. At the same time, the abrasive articles made bythe present method have greater density, reflected Iin lower' porosity and absorption, than pressed vabrasive articles of the same composition. y

The improved strength of kabrasive `articlesmade by the methodof this invention is indica# tive of av better vdistribution of the -bond'in the abrasive article, and this indication isk supported :yuplhotomicrographs made of sections vof vsuch* c es. y l v InvFlgure :2 is shown such-a photo'micrograph,

and it may be seen from this figure that the bond is distributed as lmore or less continuous films between adjacent grains of abrasive,

abrasive grain suitably compacted, anda 4.armaturesi1m1i1111r ,intim abwardesaribed tively free of bond. It 1s believedtthatflthis ms- .tributionmfthe .fbond eissfobtained by `reason of #grain istsaturated. upon away from; thefcentervofy the intergranularv spacesi into the finer channels between the' grains., thus bonding the grains more firmly while' leaving "the '-intergranular spacesropen,l .and giving-l an article i-twitli v Lsuilicient evenlyv distributed` pores' as vto tial equilibrium inra zvertical direction., "That is,`

with suitable side support` for fthe grains om` the Vouter -sidemsurface-of thearticle such `as was :initially furnished Ythe grainsin the mass by the sides oft-.the .porous'container |2,\and a suitable bottom support for the grainsconforming to the bottom surface of the article, :even ifthe bond 1 ofthefinished article were-removedfthe grains xwouldwremain 1 ixr-substantially the' same position ,which they -`have "in the finished article. 1-

i, l` In Figure 3l is shown-"a photomicrographlof a l :section lof #an labrasivetsnagging whee1`formed byithe molding methodcommonly usedandv containing what yisla-coimnon percentage of bond in `commercial; snagging wheels-25% by weight.

It. will be-seenfrom this figure thatthepropor-` ution' ,oft` 1arge,-`1.eiective`lgrainsftis much smaller than ina-Figure 2a'nd that-,the .bond occupies a considerable number of :theintergranular spaces,

thus reducing the eectiveness of; .the wheel so V--far as porosity isc-:oncer-ned'.V I f fr In:Figure` 4 is shownfa-photomicrograph of a `,xsectio'n of an abrasive snagging wheel which has been-moldedinthe:l common manner,l but t which .t--Icontainsonly approximately-17% by weight of bonen .It Vwill .be nqted,in this rieure, that the .proportion; of .small, --ineiective`- grains islarge andv. thatz the :bond is. not `fas; effectively located ff amount :of the bond -i clinging to surfaces.l of

"fthe abrasive grains1 which are not in contact,l

@andi-is thus not teilectivefin-- bonding. y 1 2 In general, it may be said thatthe structures `shown-:inv Figuresfand 4i are similar .in that the 11f-Jetfectivefgraineareal.istsmallerin both cases. than ein Figure! f3 reci-Wely diirbutfesie while.: fin k,1F-islam f 3,2 it octfcupiestooemuah ofiathetintersranular space, and finlEiaurcf; uilicient bonding enfeet, 'ecomnarison 0f y l-thes photam-.ierosraphs v:will make-ritenga that th ,entf

While there has .been "desc ducing`1-abrasive wheelslfaby allowing the penetra-4f tion upwardly through a` mass of grain of a slurry of bond ingredients, it must notbe assumed that this is the only method by which the improved articles of the present invention may" be produced. While the upward penetration is convenient, sinceit makes it easier for air to escape from the mass of grain, satisfactory articles can be obtained by other means. Thus Moreover, the bond invFigure, 2 is.

i l'll'he superiority-` Qfsnagging wh l the'prooess of the present, invention isshown hy l0L taken-to prevent the entrapment ofI air inj the massief stain. and slurryrandfit may-be desirble to vibrate the,maidl Vdurimzt'murrine of the slurry,-to assisttheescapeofair. tu f s made, by

thefact, that their .-Gutting rates are, in general,

about twice thatl ofsnaggingwheels of. Omme'r- `cialv types made l-byprior .artfmethodsl when :grinding the same; materlalunderthe same con- ;ditions. t

wnue the presentlivention has `been described particularly with respect vto the manufacture of snagging wheels, itwill be recognized that ,other types of abrasive articles and wheels can be easily vand conveniently) `made by this process, and it is not intended that the invention shall be lim- -ited to use in the makingof snagging wheels.` lWhere vibration ,has been referred to in l this specication and claims, itis meant to include not only high-frequency lvibration such, for

example; as that induced byvelectromagnetic vibrators and the. like, but also to include hammering,.jolting and other low-frequency vibrating methods.` i

The above-described yinw'mtion is intendente 1..Ihe impr y snagging wheels which comprises: treating abrasive grainof relatively large gritsize with a wet-` ting agent; placingthe, treated abrasive grain ina porous container; compacting said abrasive ,grainbysubjecting it to vibration; forminga deflocculating said slurry; immersing said abraceramicbondraw mix into a slurry with water;

sive grain-in the deocculated slurry so as to allow upward penetrationjand saturationI of,I the compacted grain by said slurry; ysubjecting the `container holdingthe grain to vibration while said abrasive grainis immersed in, said slurry:

"drying the saturatedmass ofA abrasive-grain;

` and burning the dried product to at least partially vitrify the bond. H 4 L l 2.' 'I'he improved'v process of,

making abrasive l snaggingwheelswhich comprises: treating abrasive grain of relatively large-grit size with al wetnt'ing agent placing; the treated abrasive grain in ,a porous container; compacting said abrasive grain, by subjecting; it to vibration; forming14 a t, ceramic -bond raw mix into a slurryq-withwater: A. detlocculating said eshirry;K immersinggsaid abra- Asive'- grain in` thefdeocculated`- slurry4` so asl to allow .upward penetration and ,saturation ofI fthe tcompacted grain by said slurry; dryingcthesaturated mass ,of abrasive graimLand-burning the Vdried AAprodiitttotali least IvI artiallv-,z vittiffv'tne @3.- The abrasive .snassinawheels Awhich comprisesi :placing akiravsive grain of relatively large (grit. size a porous the bond slurry may be poured into a mold con- 1l sive grain is immersed ln'said slurry: drying the 4ed process of making abrasive 4 Y l saturated masso! abrasive grain; and burning th dried product to at least partially virtify the V d. 4. The improved process of making abrasive snagging wheels which comprises: placing abrapacted grain by said slurry; drying the saturated urated mass of abrasive grain; and maturing the 'dried product.

10. The improved process of making abrasive articles which comprises: compacting a mass of abrasive grains of relatively largey grit size and mass ofabrasive grain; and burning ythe dried product to at least partiallvvvitrify the bond.

5. The improved process of making abrasive articles which comprises: treating abrasive grain with a wetting agent; placing said treated abra sive grain in a porous container; compacting said abrasive grain by subjecting vit to vibration; forming a ceramic bond raw mix into a slurry with water; `deiilocculating said slurry; immers-` ing said abrasive lgrain in' thedeilocculated slurry so as to allow upward penetration and saturation of the compacted grain by said slurry; subjecting the container holding the grain to vibration while said abrasive grain is immersed in said slurry: drying the saturated mass of abrasive'grain; and burning the dried product to at least partially vitrlfy the bond.l

6. The improved process of making abrasive articles which comprises: treating abrasive grain with a wettingagent placing said treated abrasive grain in a porous container; compacting said abrasive grain forming 'a ceramic bond raw mix into a slurry with water; deilocculatingsaid slurry: immersing said abrasive grain inthe deilocculated slurry so as t allow upward penetration and saturation of 'the compacted grain.

by said slurry; drying the saturated mass of abrasive grain; andr burning the dried product to at least partially vitrify the bond;

'1. The improved process oi making abrasive articles which comprises: placing abrasivegrain lying within a short' range of grit sizes in such a manner that 4they form a vertically self-supporting mass, lsaid abrasive grains being in'iiij` timate contact with each other,` thereafter saturating the mass of abrasive grain with av fluid dispersion of ceramic bond without substantially changing the disposition' of the abrasive grains relative to each other, drying the saturated m'ass of abrasive grain, and burning the dried product to at least partially vitrify the ceramic bond, whereby the bonding material is distributed 'as more or less'continuous iilms between adjacent grains of abrasive, there being open spaces between the grains, said open spaces being relatively free of bond.

12. A dense ceramic bonded snagging wheel rcomprising abrasive grains and matured ceramic withinl the pore spacesilexisting between the abrasive grains. ,l

13. A denseceramic bonded abrasive article comprising abrasive grains and matured ceramic in a porous container; compacting said abrasive grain: forming a slurry of bonding ingredients 8. Thefimproved process of making abrasive Narticles which comprises: placing abrasive grain.-

in a porouscontainer; compactingsaid abrasive grain; forming' a `slurry'of bondingfingredients with water; introducing said slurry into said porous container so as to saturate the compacted grain therewith; drying the saturated mass of abrasive grainy: and maturing the driedlproduct,

9. The improved process of .making abrasive articles which comprises: placing abrasive grain in a porous container; forming a dispersion of bonding ingredients; introducing said dispersion into said porous container so as. to saturate the abrasive grain therewith: drying the satbonding material, the abrasive grains in the article being of relatively coarse grain sizes and lying .within a short range of grain sizes, each grain contacting a suilicient number of other grains in the article to be supported `in substantial vertical eqiulibrium in the absence of bonding material', matured bonding material being distributed, substantially uniformly 111011 the abrasive grains as more or less continuous illms within the pore spaces existing between 4the abrasive. f

'14.' A dense ceramic bonded. abrasive article comprising abrasive grains and matured ceramic bonding material, the abrasive grains in the article being ofl relatively coarse grain sizes, each 

